NATIONAL GRID COMPANY PLC - (A wholly owned subsidiary of National Grid Transco plc)

 
 
NATIONAL GRID COMPANY PLC - (A wholly owned subsidiary of National Grid Transco plc)
National Grid Company plc                                        10 September 2003




                       NATIONAL GRID COMPANY PLC
            (A wholly owned subsidiary of National Grid Transco plc)



 Investigation Report into the Loss of Supply Incident affecting parts of South
                London at 18:20 on Thursday, 28 August 2003




   This report has been produced by National Grid Company plc (National Grid) to
record the investigation findings concerning the loss of supply in south London on 28
 August 2003. The purpose of the investigation is to enable National Grid to identify
   the cause or causes of the incident so it may seek to prevent a recurrence. The
purpose of the report is not, however, to identify legal liability; therefore the data and
  information within it have not been compiled in accordance with rules of evidence
and cannot be treated as determining either National Grid’s nor any individual’s legal
                                        liability.




                                         Page 1
NATIONAL GRID COMPANY PLC - (A wholly owned subsidiary of National Grid Transco plc)
National Grid Company plc                                            10 September 2003



Index                                                                page


Executive summary                                                    3
           Introduction
           Transmission System in South London
           Maintenance Activity in the Area
           South London Transmission System (diagram)
           The First Fault                                           4
           The Second Fault
           Restoration                                               5
           Communication
           Investigation                                             6-7
           Actions being pursued                                     7

Investigation Report                                                 9
            Introduction
            Overview of the incident
            Background                                               10
              Transmission system in south London
              (Map of affected substations)
              Investment programme in the area                       11
              (London area investment –graph)
              Key policies and procedures relevant to the incident   12

           Findings
             Operating arrangements on the day                       13-14
             (Table of circuits out of service on 28 August)
             Sequence of Events                                      14-18
             Communication during the incident                       18
             Response to the Buchholz alarm                          19
             Disconnection of the transformer                        20
             Unexpected operation of the protection                  20-21
             Maintenance of assets                                   21
             Other factors                                           22
             Configuration of EDF Energy’s substation                22-23
             Communications                                          23
             Investigation                                           24-25
             Actions being pursued                                   26


     Appendices                                                      27-43




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National Grid Company plc                                         10 September 2003



     Investigation Report into the Loss of Supply Incident affecting parts of South
                    London at 18:20 on Thursday, 28 August 2003.

                                    Executive Summary

    Introduction

1   A combination of events led to an electricity power supply failure in south London that
    occurred at 18.20 on 28 August. Restoration began at 18.26 and power supplies
    from National Grid were fully restored at 18.57. This report describes the
    circumstances leading to the loss of supply, the steps taken to restore supplies and
    the measures in hand to minimise the risk of a recurrence.


    Transmission System in South London

2   The transmission system in south London consists of four substations at Littlebrook,
    Hurst, New Cross and Wimbledon. Normal demands of around 1,100MW are drawn
    by EDF Energy to supply domestic customers and London Underground, together
    with supplies for other large users including NetworkRail. Following the incident
    supplies were lost from Hurst, New Cross and part of Wimbledon.


    Maintenance Activity in the Area

3   On 28 August 2003, scheduled maintenance was underway on one circuit from
    Wimbledon to New Cross and one from Littlebrook to Hurst. This level of
    maintenance is usual during the summer months, when demand for electricity is
    generally lower.

4   In line with normal practice, the arrangement of the transmission system to
    accommodate the maintenance had been agreed with the operator of the distribution
    system for the London region, EDF Energy, well in advance, during July 2002.
    Routine weekly communication between EDF Energy and National Grid resulted in
    the planned outage at Wimbledon proceeding on 1 July 2003. EDF Energy confirmed
    that it could arrange its distribution system to accommodate this outage securely for
    the maintenance period.

    Figure 1: Schematic of the south London transmission system
                                                                                       Northfleet
      Willesden                1                  1               1                    West
     Beddington    Wimbledon        New Cross             Hurst          Littlebrook
     Beddington                2                  2               2                    Beddington
                                                                                       & Kemsley
                                            Out of service for
                                         scheduled maintenance




                                            Page 3
National Grid Company plc                                    10 September 2003



     The First Fault

5    The sequence of events started at 18:11. Engineers at the Electricity National
     Control Centre (National Control) received an alarm indicating that a transformer, or
     its associated shunt reactor, at Hurst substation was in distress and could fail,
     potentially with significant safety and environmental impacts. This “Buchholz alarm”,
     told National Control that gas had accumulated within the oil inside the equipment,
     which can lead to a major failure. National Grid has approximately 1,000
     transformers with associated equipment connected to its transmission system and on
     average only 13 Buchholz alarms are received each year.

6    National Control contacted EDF Energy to discuss the Buchholz alarm and asked
     EDF Energy to disconnect the distribution system from the transformer. Then, as is
     normal practice in this situation, National Control initiated a switching sequence to
     disconnect the transformer from the transmission system. This switching sequence
     temporarily left supplies dependent on a single transmission circuit from Wimbledon
     that feeds New Cross and Hurst substations. Under National Grid operating
     procedures a Buchholz alarm is sufficiently serious to warrant the isolation of
     equipment and reduced security is acceptable for “switching time”. This is a period of
     time, normally around five to ten minutes, during which the transmission system is
     rearranged, by connecting and disconnecting circuits, so that the affected equipment
     can be taken out of service.

7    The switching sequence to remove the transformer began at 18:20, disconnecting
     Hurst substation from Littlebrook substation. This enabled a safe shutdown of the
     transformer which had suffered the alarm, but left Hurst supplied only from
     Wimbledon via New Cross.


     The Second Fault

8    Unexpectedly, a few seconds after the switching, the automatic protection equipment
     on the number two circuit from Wimbledon to New Cross operated, interpreting the
     change of power flows, due to the switching, as a fault.

9    The transmission system is extensively fitted with many levels of automatic protection
     equipment, aimed at isolating faults and preventing damage to equipment or even a
     complete shutdown of the transmission system.               They measure system
     characteristics, such as voltage and current and, in the event of a fault, will
     automatically disconnect affected equipment. On the National Grid transmission
     system there are approximately 43,000 such pieces of equipment, each with its
     individual settings to meet local requirements.

10   The automatic protection relay disconnected the circuit from Wimbledon to New
     Cross. This disconnected New Cross, Hurst and part of Wimbledon from the rest of
     the transmission system, causing the loss of supply. 724MW of supplies were lost,
     amounting to around 20% of total London supplies at that time. This affected around
     410,000 of EDF Energy’s customers, with supplies being lost to parts of London
     Underground and NetworkRail.


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National Grid Company plc                                    10 September 2003

     Restoration

11   Restoration actions began at 18:26, re-energising the Hurst substation from
     Littlebrook and then isolating the Wimbledon to New Cross circuit, that had
     automatically disconnected itself, to prevent a recurrence.

12   At 18:38 National Control offered to restore supplies to Wimbledon for EDF Energy.
     EDF Energy requested restoration of that supply at 18:48 and restoration was
     completed at 18:51. From this point onwards, London Underground could restore
     electricity to the underground network, when they considered it was safe to do so.

13   At 18:41 EDF Energy restored supplies via National Grid’s Hurst substation to
     approximately one third of the consumers.

14   Some 30 switching actions enabled National Grid to restore overall supplies to all
     substations concluding with New Cross at 18:57 which restored the remaining
     supplies for NetworkRail. The substations remained connected to the rest of the
     transmission system via a single circuit until 23:00, the time at which the automatic
     protection equipment that had operated at Wimbledon was successfully isolated.
     The number two circuit from Wimbledon to New Cross was then safely returned to
     service and normal levels of security were restored. A rapid check was made to
     similar automatic protection equipment.


     Communication

15   During the incident there was significant operational communication between
     National Grid and EDF Energy. Communications were initiated at 18:17, following
     the Buchholz alarm being reported, and EDF Energy were requested to remove the
     demand from the transformer. At 18:21 EDF Energy called National Grid to confirm
     that there was a problem on the transmission system.

16   Such operational communications continued throughout the restoration, with
     continuous telephone conversations between control engineers at National Grid and
     EDF Energy’s control centre, working together to reconnect the affected area. Some
     17 minutes later National Grid offered to restore supplies to Wimbledon and New
     Cross.

17   At 18:51 National Grid was called by New Scotland Yard and National Control
     informed them that this was a system incident with no third party involvement.

18   The complex and rapidly changing chain of events affected a large number of
     organisations. In the wider communication exercise through Thursday night and
     Friday, in addition to briefing the media, National Grid was in contact with the
     emergency services, the DTI, Ofgem, the London Mayor, energywatch and others.




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National Grid Company plc                                      10 September 2003

     Investigation

19   The planning of maintenance works had been carried out in accordance with National
     Grid’s policies and that the maintenance work could not be regarded as a cause of
     the incident. The investigation confirmed that the transmission system arrangement
     and the communication with the distribution system operator regarding this
     maintenance complied with the relevant National Grid planning standards and
     operating procedures.

20   All actions in configuring and switching the transmission system complied with
     National Grid’s planning standards and operating procedures and that the restoration
     process was carried out quickly and professionally without further incident. The
     response by control engineers to re-secure the network and restore the balance of
     generation and demand ensured that the disturbance was contained within the
     affected substations.

21   The reason that the second fault occurred was that an incorrect protection relay was
     installed when old equipment was replaced in 2001. This incorrect installation was
     not discovered despite extensive quality control and commissioning procedures
     followed by both supplier’s and National Grid’s specialist staff. This piece of
     equipment has been replaced. Once the cause was known an extensive survey of
     similar equipment was immediately initiated. To date 20% (9,000 items) of this type
     of equipment on the National Grid system has been surveyed and there have been
     no similar cases. The remaining equipment will be surveyed within four weeks.

22   The engineers involved in the commissioning of the automatic protection equipment
     had the appropriate training, authorisation, experience and skills to undertake the
     task. There is evidence that the detailed commissioning procedures were followed
     correctly at all stages and that no part of the process had been omitted. However,
     the rating of the automatic protection equipment that is included on the
     documentation used for commissioning could have been more clearly visible to the
     commissioning engineers.

23   The actions to remove the Hurst transformer did not directly contribute to the cause
     of the incident. The consequential increase in flows on the Wimbledon to New Cross
     circuit, which were within operational limits, initiated the operation of the protection
     relay at Wimbledon. National Grid engineers would not expect their actions to
     remove the equipment would have caused the loss of supply.

24   The impact of the incident on the areas of south London was exacerbated by the loss
     of supplies to underground and railway transport services.

25   From the 20 July, EDF Energy’s distribution system was arranged such that a
     significant supply to London Underground was dependent on a single transmission
     circuit. This meant that in the event of a fault occurring on one of National Grid’s
     transformers at Wimbledon the distribution system configuration would result in a loss
     of supply. However, National Grid understands that EDF Energy had contingency
     arrangements for immediate restoration of supplies to London Underground in such
     an eventuality.



                                             Page 6
National Grid Company plc                                    10 September 2003

26   Following normal practice, during the incident there was extensive communication
     between National Control and the EDF Energy Control Centre, with both control
     rooms working effectively together during the incident.


     Actions being pursued

27   This is the largest loss of supply from National Grid for over ten years and the
     company has expressed its deep regret. This incident involved a number of other
     parties and National Grid will be working closely with them in the coming weeks to
     examine the consequences and identify improvements in systems or procedures.
     National Grid has reviewed its part in the incident and is committed to the following
     steps:

        ·   National Grid will work closely with other network operators to identify
            any improvements in co-ordination to enhance the overall security of
            electricity supplies, particularly to city centres and transport systems.

        ·   National Grid will work closely with EDF Energy, the Mayor, London
            Underground, NetworkRail and other London emergency and public
            service agencies to establish improved and more responsive
            communications in the event of major loss of supply.

        ·   National Grid is urgently surveying all installations as a further check on
            the integrity of the automatic protection equipment.

        ·   National Grid will carry out a further comprehensive investigation
            examining all aspects of the management of the protection systems so
            as to eliminate, as far as possible, the risk of incorrect installation or
            operation of automatic protection equipment.

        ·   National Grid will work to review operational procedures, and control
            room systems, including alarm presentation, in close consultation with
            Ofgem, DTI and other associated parties, to ensure that there is the right
            balance between safety risks and supply security.




                                           Page 7
National Grid Company plc                                       10 September 2003




                       NATIONAL GRID COMPANY PLC
            (A wholly owned subsidiary of National Grid Transco plc)



 Investigation Report into the Loss of Supply Incident affecting parts of South
                London at 18:20 on Thursday, 28 August 2003




   This report has been produced by National Grid Company plc (National Grid) to
record the investigation findings concerning the loss of supply in south London on 28
 August 2003. The purpose of the investigation is to enable National Grid to identify
   the cause or causes of the incident so it may seek to prevent a recurrence. The
purpose of the report is not, however, to identify legal liability; therefore the data and
  information within it have not been compiled in accordance with rules of evidence
and cannot be treated as determining either National Grid’s nor any individual’s legal
                                        liability.




                                         Page 8
National Grid Company plc                                      10 September 2003

      Investigation Report into the Loss of Supply Incident affecting parts of South
                     London at 18:20 on Thursday, 28 August 2003


     INTRODUCTION

28   National Grid Company plc (National Grid), a wholly owned subsidiary of National
     Grid Transco plc, transports electricity and balances the system on a second by
     second basis. National Grid delivers electricity from generators and interconnectors
     to 12 distribution network operators for local distribution to over 24 million consumers
     and directly to a small number of large industrial users. National Grid is the sole
     holder of an electricity transmission licence for England and Wales and has a
     statutory duty under the Electricity Act 1989 (as amended by the Utilities Act 2000) to
     develop and maintain an efficient, coordinated and economical system of electricity
     transmission and to facilitate competition in the supply and generation of electricity.


     OVERVIEW OF THE INCIDENT

29   On 28 August 2003, two events occurred on the National Grid electricity transmission
     system in south London, resulting in an electricity supply failure on the transmission
     system from 18.20 until 18.57.

30   The loss of supply occurred following a switching operation to remove a transformer
     at Hurst 275kV substation from the transmission system in response to an indication
     that a serious alarm had been activated on the transformer or its associated shunt
     reactor. Actions were taken to remove the transformer from the system which
     required a controlled disconnection of the circuit between Littlebrook and Hurst. For
     a short period of 5 to 10 minutes (switching time) this resulted in the supply at New
     Cross, Hurst and parts of Wimbledon being dependent on a single transmission
     circuit. Within seconds of this operation the circuit between Wimbledon and New
     Cross substations automatically disconnected itself. The combination of these two
     events was to isolate Hurst, New Cross and a part of Wimbledon 275kV substations
     from the main transmission system, disconnecting 724MW of supplies to EDF
     Energy’s distribution network.

31   The loss of supply affected 410,000 of EDF Energy’s customers in an area of south
     London approximately bounded by Bexley in the east, Kingston in the west, Bankside
     in the north and Beckenham in the south, and led to significant disruption to London
     Underground and NetworkRail. Supplies from the transmission system to EDF
     Energy were restored within 37 minutes.

32   Roger Urwin, National Grid Transco’s Chief Executive Officer initiated a incident
     investigation chaired by Nick Winser, Group Director Transmission and Chief
     Executive of National Grid Company plc.

33   This is the outcome of the incident investigation into the events of the 28 August
     2003.




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National Grid Company plc                                    10 September 2003

     BACKGROUND

     The transmission system in south London

34   The National Grid transmission system provides an integrated network for the bulk
     transfer of power across England and Wales. The transmission system, which is
     operated at 400,000 volts and 275,000 volts, connects major power stations and
     delivers electricity to the regional distribution networks. The peak demand on the
     England and Wales transmission system is around 54,400MW. The demand for
     electricity in the Greater London area represents about 20% of the total transmission
     system demand in England and Wales.

35   The transmission system has been designed and built for an expected life of between
     15 years and 80 years, depending on the type of asset.

36   There are no large generation stations connected directly to the transmission system
     in the Central London area, although large power stations exist close to London at
     Barking, Grain, Littlebrook and Kingsnorth. The transmission system facilitates the
     transmission of power from these and more remote generating stations to London.

     Figure 2: Transmission system in south London




                    © Crown Copyright, National Grid Transco EL273384

37   The south London 275kV network between Wimbledon and Littlebrook is shown in
     the above figure. The network is made up of substations, which include switchgear,
     transformers, shunt reactors and protection and control equipment. These are
     connected by circuits comprising overhead lines and cables. A description of the
     assets that make up the south London network is provided in appendix 1.




                                           Page 10
National Grid Company plc                                                      10 September 2003

     Investment Programme in the Area

38   Since 1990, around £3,600m has been invested in the National Grid transmission
     system. Of this, approximately £700m has been invested in the transmission system
     in the Greater London area.

39   Major elements of this work include connection works for new generation at Barking
     and Kingsnorth, construction of two new substations at West Ham and St Johns
     Wood, and major infrastructure reinforcement including the new 20km cable between
     Elstree and St Johns Wood.

40   Since 1995/96 investment in the London area has been increasing and has been
     around £100m per year for the last 2 years as the new Elstree-St Johns Wood tunnel
     and cable circuit has been constructed.

     Figure 3: Investment in the London area

                                             London Area Investment

                            120

                            100

                            80
               £m Outturn




                            60

                            40

                            20

                             0
                                  95/96   96/97   97/98    98/99    99/00   00/01   01/02   02/03



41   Of the investment in the London area, around £75m has been invested in the
     Littlebrook to Wimbledon 275kV system and the adjacent network in south London.
     Specific projects have included:

        ·   Supply point reinforcement works at Littlebrook and New Cross
        ·   275kV cable works on the circuits between between Hurst, New Cross and
            Wimbledon over the period 1995 to 2002
        ·   Works to provide a new tunnel under the River Thames at Dartford and new
            275kV cables for the Littlebrook to West Thurrock 275kV circuits
        ·   Switchgear replacement
        ·   Automatic protection and control system replacement.
        ·   Environmental improvement works at several sites, such as enhancing oil
            containment works.

42   As part of National Grid’s planned asset replacement programme, future work in the
     Littlebrook to Wimbledon 275kV system and the adjacent network in south London

                                                          Page 11
National Grid Company plc                                   10 September 2003

     includes the replacement of shunt reactors, replacement of the Beddington-Rowdown
     275kV cable, the extension of the supply point at New Cross and improvements to
     cable cooling systems and joint bays.

43   The average expenditure in the London area is planned to be over £50m per year
     over the next 5 years.

44   There has been a considerable investment programme in the transmission
     system in and around London since 1990, and this programme is set to
     continue at a high level in future years.


     Key Policies and Procedures Relevant to the Incident

45   As part of National Grid’s responsibility to operate a safe, secure and reliable
     transmission system it has a responsibility to ensure that the asset related safety,
     environmental and operational risks are managed and acceptable. In addition, the
     company has an obligation to carry out this duty in an efficient manner. To this end
     National Grid has developed an asset management approach which uses a
     combination of maintenance, refurbishment and replacement strategies. The
     procedures, which provide a framework for the delivery of this approach, are well
     established and defined and subject to external audit as part of National Grid’s ISO
     9001 accreditation. Details on National Grid’s maintenance, asset replacement and
     commissioning policy are included in appendix 2.




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National Grid Company plc                                            10 September 2003


     FINDINGS

     Operating Arrangements on the day

46   On the evening of Thursday 28 August 2003, the transmission system in the south of
     London was secure and was operating in accordance with the relevant National Grid
     planning standards and operating procedures (Appendix 3 provides details). The
     substations were all configured in a secure manner supplying normal demands of
     around 1,100MW.

47   The transmission system in the area was arranged with a number of circuits out of
     service for scheduled maintenance.

      Circuit                       Reason                                            Dates
                                    Installation of thermal monitoring on cables,
      Number two circuit from                                                         26 August to
                                    maintenance of circuit breakers and other
      Littlebrook to Hurst                                                            19 September
                                    planned maintenance at Hurst and Littlebrook
                                    Major refurbishment of the cables and
      Number one circuit from                                                         1 July to
                                    installation of new protection and control
      Wimbledon to New Cross                                                          28 September
                                    systems

48   The Wimbledon, New Cross and Hurst substations, that were to be affected by the
     incident, were connected to the rest of the transmission system by two circuits,
     ensuring that a single transmission fault would not result in a loss of supply.

49   A simple diagram of the transmission network in this area of London is illustrated in
     the figure below.

     Figure 4: Schematic of the Transmission System in South London
                                                                                           Northfleet
       Willesden                1                     1               1                    West
      Beddington    Wimbledon           New Cross             Hurst          Littlebrook
      Beddington                2                     2               2                    Beddington
                                                                                           & Kemsley
                                                Out of service for
                                             scheduled maintenance


50   If a fault did occur and left supplies dependent on a single transmission circuit, in
     most cases, National Grid was able to restore security of supply within switching time
     or by returning one of the circuits that was out on maintenance.

51   To maintain an efficient transmission system it is necessary to undertake planned
     maintenance. The disconnection of circuits and network configuration is planned and
     agreed following a rigorous process that involves studies to both optimise the
     coordination of outages with parties connected to the system and to ensure the
     network configuration is secure against all credible faults that may occur.

52   The planning process to agree these outages and the configuration of the system
     began in July 2002. As part of the process regular liaison meetings were held and
     exchanges of information undertaken with EDF Energy (on a daily basis in the last
     two months). These discussions concluded in a formal agreement for the release of

                                               Page 13
National Grid Company plc                                                    10 September 2003

     the circuits before the work was due to commence. As is normal, the maintenance
     schedules of both EDF Energy and National Grid were subject to change during the
     early part of the summer. EDF Energy were fully engaged in this process and fully
     aware of the configuration of the transmission system and its impact on its system.
     As part of this process the contingency plans for EDF Energy’s 132kV Wimbledon
     substation were discussed, as the planned outage would entail a reduction in the
     number of feeds from the National Grid transmission system from four to three.
     National Grid understood that due to limitations on the EDF Energy’s system, some
     distribution supplies from Wimbledon would be dependent on a single transmission
     circuit. National Grid understands that in the event of the loss of this transformer
     EDF Energy’s post fault action would be to immediately switch its Wimbledon Grid
     132kV substation to reinstate supplies, from the remaining two National Grid
     transformers.

53   If the circuits that were out for maintenance had been available, clearly there would
     have been no loss of supply. However maintenance is an essential part of sustaining
     an efficient transmission system and to increase security above the current standards
     would require a huge investment in new transmission assets.

54   The investigation confirmed that the configuration of the transmission system
     was not a contributory factor to the loss of supply.


     Sequence of Events

55   The sequence of events commenced on Thursday 28 August at 18:11 when an alarm
     was received at the Electricity National Control Centre (National Control) at
     Wokingham. The system configuration at the start of the incident and the power
     flows are illustrated below.

     Figure 5: Transmission system configuration and power flows

                                                                                486 MW
                                                                                                         Northfleet
       Willesden                     1                     1                      1                      West
      Beddington     Wimbledon              New Cross               Hurst                 Littlebrook
      Beddington                     2                     2                      2                      Beddington
                                   72 MW                                                                 & Kemsley
                   Supplying EDF           Supplying EDF        Supplying EDF            Supplying EDF
                   478 MW                  359 MW               199 MW                   84 MW

                                                     Out of service for
                                                  scheduled maintenance


56   The sequence of events during the incident is described below. The detailed switch
     operations is attached in appendix 4.

57   At 18:11 staff at the National Control received an indication that a transformer or
     shunt reactor at Hurst substation was in distress and could fail, with potentially
     significant safety and environmental impacts. The indication, called a “Buchholz
     alarm”, told National Control that gas had accumulated within the oil inside the
     transformer or shunt reactor, which can lead to equipment failure.


                                                   Page 14
National Grid Company plc                                                     10 September 2003

58   At 18:17 discussions were held with EDF Energy regarding the Hurst transformer or
     shunt reactor. National Control informed EDF Energy that the transformer was to be
     switched out of service. To achieve this the transmission system had to be
     rearranged by switching equipment and circuits in and out, so the affected equipment
     could be safely and securely taken out of service. During switching time (typically 5 –
     10 minutes) one circuit would supply New Cross and Hurst substations.

59   EDF Energy confirmed that they had disconnected the transformer from the
     distribution system. There was no impact on supplies to EDF Energy as these
     remained connected to Hurst substation via two other transformers.

60   The immediate priority was security of supplies. At 18:19 the circuit from Littlebrook
     to Beddington and Kemsley was switched in. This reconfiguration of the network
     ensured power flows at Littlebrook substation would be secure once the number one
     circuit from Hurst to Littlebrook was switched to take the Hurst transformer and
     associated Hurst shunt reactor three out of service.

61   At 18:20 two circuit breakers were opened at Hurst to remove the transformer or
     shunt reactor from service. At this point, the Hurst and New Cross substations were
     supplied from Wimbledon 275kV substation and were dependent on the single,
     number two circuit, from Wimbledon to New Cross.

     Figure 6: Transmission system at 18.20
                                                                                                        Northfleet
       Willesden                     1                       1                    1                     West
      Beddington     Wimbledon               New Cross               Hurst                Littlebrook
      Beddington                     2                       2                    2                     Beddington
                                   558 MW                                                               & Kemsley
                   Supplying EDF            Supplying EDF        Supplying EDF          Supplying EDF
                   478 MW                   359 MW               199 MW                 84 MW

                                            Out of service for
                                                                         National Control action
                                         scheduled maintenance


62   Immediately following the opening of the two circuit breakers at Hurst, the automatic
     protection relay operated on the number two circuit from Wimbledon to New Cross
     automatically opening two circuit breakers at Wimbledon and removing the number
     two circuit from Wimbledon to New Cross from service. This isolated New Cross,
     Hurst and part of Wimbledon substations from the rest of the system. All supplies
     were lost at Hurst and New Cross substations and 35% of the supplies were also lost
     to EDF Energy’s Wimbledon Grid 132kV substation. Two transformers at Wimbledon
     continued to supply Wimbledon Grid 132kV substation.

63   The transmission network was now configured as in the diagram below.




                                                    Page 15
National Grid Company plc                                                       10 September 2003

     Figure 7: Transmission system immediately following the incident
                                                                                                        Northfleet
       Willesden                           1                    1                    1                  West
      Beddington         Wimbledon              New Cross                Hurst            Littlebrook
      Beddington                           2                    2                    2                  Beddington
                                                                                                        & Kemsley
                       Supplying EDF           Supplying EDF         Supplying EDF       Supplying EDF
                       166 MW lost             359 MW lost           199 MW lost         84 MW maintained
                       312 MW maintained

                      Out of service for
                                                       National Control action             Automatic action
                   scheduled maintenance




64   Following the event EDF Energy transferred 72MW of demand supplied by
     Wimbledon Grid 132kV substation to another supply point by reconfiguring the
     distribution network.

65   Assessing the alarms received, National Control concluded that the automatic
     protection equipment on the number two circuit from Wimbledon to New Cross had
     most likely operated incorrectly.

66   At 18:21 National Control and EDF Energy discussed the loss of supply and the
     substations affected.

67   At 18:22 standby engineers were called out to Wimbledon, New Cross and Hurst
     substations to investigate and help restore supplies.

68   At 18:23 National Control commenced the sequence of operations to restore security
     for the remaining transmission system and restore supplies. It was decided to keep
     the number two circuit from Wimbledon to New Cross out of service until the cause of
     the operation of the automatic protection relay was established, as it was highly
     probable that if switched into service the automatic disconnection would recur.

69   At 18:25 the network was reconfigured to isolate the number two circuit from
     Wimbledon to New Cross, while Wimbledon substation was fully energised by closing
     the two circuit breakers which had automatically opened following the earlier
     operation of the automatic protection equipment. These actions re-secured the
     transmission system against further faults, minimising the chance of further losses of
     supply. Due to uncertainty over the cause of the protection operation, the re-
     energised transformer feeding Wimbledon Grid 132kV substation was not
     immediately made available to EDF Energy, although two transformers at Wimbledon
     capable of carrying the entire demand remained in service throughout the incident.

70   Having re-secured the system at 18:25 the restoration strategy was to configure the
     network for a phased re-energisation starting at Littlebrook. A complex switching
     sequence was required to prepare the transmission and distribution network and
     ensure that the risk of further faults was minimised by carefully switching cable
     circuits to control the voltage.

71   By 18:30 further reconfiguration of the network had taken place and the first sections
     of Hurst and New Cross substations had been re-energised.


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National Grid Company plc                                    10 September 2003



72   At 18:31 National Control confirmed those developments to EDF Energy Control and
     informed them that it would contact them soon to start restoring supplies.

73   At 18:38 National Control informed EDF Energy Control that supplies could be
     restored to Wimbledon Grid 132kV substation. During the same conversation
     National Control also informed EDF Energy Control that supplies at New Cross could
     be restored. At this time EDF Energy Control requested time to assess the
     distribution network and agreed to call back.

74   By 18:40 further reconfiguration of the network had taken place energising further
     sections at New Cross and Hurst.

75   At 18:40 National Control contacted EDF Energy Control to offer restoration of
     supplies at Hurst. EDF Energy reconfigured the distribution network and EDF
     Energy’s Bromley supplies were restored at 18:44. This restored approximately a
     third of the 410,000 customers lost at 18:20.

76   Between 18:44 and 18:50 further reconfiguration of the transmission system took
     place.

77   At 18:48 EDF Energy Control contacted National Control to complete restoration of
     supplies to the Wimbledon Grid 132kV substation. At 18:52 all remaining supplies to
     Wimbledon Grid 132kV substation were restored.

78   At 18:51 a further Buchholz alarm was received relating to the transformer or shunt
     reactor at Hurst. No indications were received that the transformer had been
     disconnected by automatic protection, indicating that the shunt reactor was the faulty
     equipment.

79   At 18:51 New Scotland Yard contacted the National Grid control room and it was
     confirmed that the loss of supply was a system incident, with no third party
     involvement.

80   At 18:52 National Control contacted EDF Energy Control to restore supplies at New
     Cross. EDF Energy Control requested time to assess the distribution network prior to
     restoring supplies and agreed to call back.

81   At this stage 29 switching operations had been planned and successfully executed in
     26 minutes.

82   At 18:56 EDF Energy Control called National Control back and EDF Energy supplies
     to New Cross were restored at 18:57. At this point all supplies from the transmission
     system were available to the distribution network.

83   At 19:10 EDF Energy Control contacted National Control and asked for the Hurst
     transformer to be returned to increase security on the distribution network. The
     original Buchholz alarm was attributable to the shunt reactor at Hurst which was
     isolated and the transformer was made available to EDF Energy Control.



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National Grid Company plc                                                         10 September 2003

84   At 19:14 EDF Energy Control confirmed all supplies to consumers had been
     restored.

85   During the period 19.00 to 19.45 standby site engineers arrived at the three sites. On
     arrival each standby engineer checked protection relay indications and alarm logs
     and confirmed the situation with National Control. To support the restoration process
     and initial investigation, two further engineers were also called to attend site.

86   The network was now configured as follows:

     Figure 8: Transmission system after restoration

                                                                                     437 MW
                                                                                                              Northfleet
       Willesden                           1                    1                      1                      West
      Beddington         Wimbledon              New Cross                Hurst                 Littlebrook
      Beddington                           2                    2                      2                      Beddington
                                                                                                              & Kemsley
                       Supplying EDF           Supplying EDF         Supplying EDF            Supplying EDF
                       422 MW                  262 MW                175 MW                   84 MW


                      Out of service for
                                                       National Control action                  Automatic action
                   scheduled maintenance


87   At 20:02 restoration of all supplies was confirmed with New Scotland Yard.

88   At 20:55 EDF Energy Control requested a formal report on the incident.

89   After assessment by engineers on site at Wimbledon, it was confirmed the automatic
     protection relay had been taken out of service and the number two Wimbledon to
     New Cross circuit was returned to service at 23:00. This action further enhanced
     security at Wimbledon and Hurst. No further switching was carried out to allow the
     system to be re-assessed and minimise the risk of any further faults. Full security
     was completed by reconfiguring the network overnight, with full security re-
     established at 01:05 on 29 August.

90   The Standby engineers called to site remained on each site until restoration was
     complete.

91   Following the initial loss of supply National Control engineers correctly
     assessed the risks and restored transmission supplies within 37 minutes.


     Communication during the incident

92   Throughout the incident close communication was maintained between National
     Control and EDF Energy. Communications relating to this incident commenced at
     18:17 following receipt of the initial alarm and were maintained throughout the
     incident and well into the night. In addition, National Control received a call from New
     Scotland Yard, and confirmed that this was a system incident.



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National Grid Company plc                                     10 September 2003

93   The incident generated substantial media interest, with National Grid handling some
     300 media calls on Thursday evening.

94   A verbal statement was given to journalists within 25 minutes of the incident. Written
     media statements were issued at 21.25 on Thursday evening and 13.30 on Friday
     afternoon.

95   During a major incident, National Grid would normally communicate with bodies such
     as Ofgem, DTI, energywatch and others with a direct interest, depending on the
     incident. Contact was made with Ofgem, DTI and other parties as soon as possible
     during the incident and communication continued through the evening and the
     following days.

96   Following the event there were high-level contacts with Ofgem, the Energy Minister,
     DTI officials, the Mayor of London, EDF Energy and energywatch, among others.


     Response to the Buchholz Alarm

97   National Control actions were in line with National Grid procedures for responding to
     an indication that a Buchholz alarm had been activated on a transformer or shunt
     reactor at Hurst 275kV substation.

98   The causes and implications of a Buchholz alarm are set out in appendix 5, but in
     summary, the alarm provides a warning of potential problems in the transformer or its
     associated shunt reactor that could result in a major failure. Hence, due to the nature
     of the consequences of such a failure, National Grid procedures specify the
     equipment is to be disconnected from the transmission system, except in a limited
     number of circumstances. These exceptions include any action that would result in a
     loss of supply.

99   As is normal in the design of control room systems, to avoid “alarm flooding” in the
     event of major system incidents, alarms are combined to reduce the total number
     displayed in the control room. The investigation noted that the grouping and
     nomenclature of the alarms for the transformer and shunt reactor did not clearly
     indicate whether the transformer or the associated shunt reactor was the origin of the
     gas alarm.

100 When the alarm was received, National Control took immediate action to begin the
    process to remove the transformer by asking EDF Energy to disconnect it from the
    distribution system.




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National Grid Company plc                                     10 September 2003


     Disconnection of the Transformer

101 National Control undertook further switching actions in order to disconnect the
    transformer from the transmission system. The specific design of the substation,
    called a “mesh”, required the disconnection of the circuit from Littlebrook to Hurst.
    The switching plan undertaken was in accordance with National Grid procedures on
    operating mesh substations which, for the five to ten minutes taken to switch, left the
    electricity supply at New Cross and Hurst substations dependent on a single circuit.

102 The disconnection of the Littlebrook to Hurst circuit re-routed power and as expected
    increased the power flows on the number two circuit from Wimbledon to New Cross
    from 72MW (213MVA) to 558MW (695 MVA). This is comfortably within the design
    ratings of 815 MVA for the circuit.

103 The investigation confirmed that the operational decision to switch out the Littlebrook
    to Hurst circuit and supply Hurst and New Cross from a single circuit from
    Wimbledon, for the five to ten minutes required to complete the switching, was in
    accordance with operating procedures and took account of the need to remove the
    safety risk of a major failure of a transformer.

104 The investigation has also confirmed that the configuration and capability of the
    system was in accordance with National Grid’s standards and procedures, and that
    National Grid undertakes an average of 2,700 annual switching operations at mesh
    corners without incident.

105 The investigation has found that National Grid engineers would not expect
    their actions in removing the equipment to have caused a loss of supply.


     Unexpected Operation of the Protection

106 At National Grid’s Wimbledon substation, the automatic protection equipment
    associated with the number two circuit from Wimbledon to New Cross, detected the
    change in power flows as a result of the switching at Hurst, as a fault. The protection
    equipment disconnected the circuit to prevent damage to other equipment and/or the
    propagation of the fault through the transmission system.

107 In this case the protection relay that operated was being used for backup protection.
    Backup protection is fitted to the transmission network, in conjunction with the main
    protection and is designed to disconnect faults not cleared by the main protection
    equipment.

108 The protection equipment that operated was an Inverse Definite Minimum Time
    (IDMT) relay, a commonly used type. It does not operate immediately, but starts to
    operate when the electric current on the circuit exceeds a certain threshold. The
    speed of operation depends on how far the measured current is above the threshold
    level.

109 The protection relay had been correctly specified during the design process and the
    settings sheet had been correctly produced. However the relay that had been
    physically supplied and installed at Wimbledon was a 1 ampere rated relay, not the 5

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National Grid Company plc                                     10 September 2003

     ampere relay specified on the settings sheet. In all other respects the settings on the
     relay were correct and were confirmed during several check points in the
     construction and commissioning process.

110 The effect of installing a 1 ampere relay instead of a 5 ampere, meant that the
    current flow at which the protection would operate was five times lower than the
    correct rating and below the rating of the circuit itself.

111 The 1 ampere protection relay was set to operate at a current of 1,020 amperes on
    the transmission circuit and was triggered on the day by a current of 1,460 amperes.
    This is significantly below the operating capability of the cable, at 4,450 amperes and
    the original specification of the protection relay, at 5,100 amperes (see appendix 6).

112 The protection relay was commissioned in June 2001 as part of a replacement
    scheme. Following a survey conducted as a result of the incident, all the automatic
    protection equipment in the area was surveyed and found to be correctly installed. A
    full survey of similar equipment at all substations in England and Wales has been
    initiated, and to date, having completed 20% of the total, no further cases have been
    revealed.

113 The incident investigation found that despite rigorous processes for commissioning
    protection equipment, the wrong protection relay was installed and commissioned at
    Wimbledon substation and this caused the number two circuit from Wimbledon to
    New Cross to automatically disconnect unexpectedly, and caused the loss of supply.

114 The commissioning of the automatic protection equipment involved a number of
    stages as set out in appendix 2. The investigation has found evidence to support
    that the relay settings had been correctly calculated. The setting sheets were
    correctly produced and signed by both the engineer who calculated the settings and
    the engineer who confirmed the application of those settings to the protection
    equipment. Furthermore the investigation confirmed the protection equipment had
    been tested by the manufacturer in accordance with industry practice, and that pre-
    energisation inspection tests were carried out. There is evidence that the rating of
    the automatic protection equipment that is included on the documentation used for
    commissioning could have been more clearly set out and hence visible to the
    commissioning engineers. The investigation found no evidence that any part of the
    commissioning process had been omitted.

115 The investigation has found that the direct cause of the loss of supply was the
    incorrect operation of a backup protection relay on the number two circuit from
    Wimbledon to New Cross.


     Maintenance of Assets

116 National Grid has an established maintenance policy and the assets involved in the
    incident have all been maintained according to that policy.

117 The following table summarises the maintenance undertaken on the assets involved
    in the incident at Wimbledon and Hurst.


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National Grid Company plc                                     10 September 2003


     Item Description                Last Maintenance          Next scheduled
                                     undertaken                maintenance
     Number two circuit from
     Wimbledon to New Cross,         Commissioned 2001         2007
     backup protection
     Hurst Transformer 3             September 02              2006
     Hurst Transformer 3 Shunt
                                     March 03                  2009
     Reactor

118 The investigation found that an appropriate level of maintenance had been
    carried out on the assets and poor asset condition was not a contributing
    factor to this incident.


     Other Factors

119 The investigation has determined that together with the above factors that are directly
    attributable to the operation of the transmission system, there were a number of other
    factors, external to the transmission system, that may have contributed to the
    duration or scale of the incident.


     Configuration of EDF Energy’s Wimbledon Grid 132kV Substation

120 EDF Energy own and operate the 132kV substation at Wimbledon, which is
    physically located on different site to National Grid’s substation. Maintenance
    outages were agreed between National Grid and EDF Energy as part of a well
    defined process and significant information was exchanged on network configuration
    and contingency plans for faults.

121 Four transformers from National Grid’s 275kV substation at Wimbledon supply EDF
    Energy’s 132kV substation. Normally all four transformers are connected ensuring
    that supplies can be maintained for the loss of any one transformer. National Grid
    understands that EDF Energy splits its Wimbledon substation into two parts to
    reduce fault currents and prevent over-stressing the equipment. Normally, with two
    transformers supplying each part.

122 When National Grid requires one of the transformers to be taken out of service for
    maintenance, EDF Energy configures its network with one transformer on one part
    and two on the second (figure 9). Two transformers supply the majority of demand
    for Wimbledon and Wandsworth. The remaining transformer supplies the remaining
    demand at Wimbledon and Wandsworth, together with demand at Lots Road for
    London Underground.

123 If one transformer is out of service for maintenance the Lots Road circuits will always
    be dependent on a single transmission circuit, because they can only be connected
    to the single transformer.




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National Grid Company plc                                              10 September 2003

     Figure 9: Configuration of EDF Energy's distribution system

                     National Grid           EDF Energy                    London
                                                                         Underground
                      Wimbledon
                        275kV

                                                                           Lots Road


                                            Wimbledon
                                            Grid 132kV


                                         Out of Service for scheduled maintenance


124 The configuration of Wimbledon Grid 132kV substation on 28 August 2003 is
    illustrated in the diagram above. National Grid maintained supplies to the section
    connected to transformers two and four throughout the incident.

125 National Grid understands that when one of its transformers is out of service and in
    the event of a fault on the remaining transformer, the normal arrangement would be
    for EDF Energy to connect the two parts of the Wimbledon Grid 132kV substation.
    However, National Grid does not know whether, in these particular circumstances,
    EDF Energy would have been able to take such post-fault action.

126 The investigation found that the configuration of the EDF Energy’s distribution
    system was not a contributory factor to the initiation of the incident. However,
    a more rapid implementation of post-fault actions or an alternative
    configuration could have mitigated the overall impact of the incident, reducing
    the duration and perhaps the scale of the loss of supply.


     Communications

127 Following normal practice, during the incident there was extensive communication
    between National Control and the EDF Energy Control Centre. Communications
    were initiated at 18:17, when the initial Buchholz alarm was reported, and EDF
    Energy were requested to remove the demand from the transformer. At 18:21 EDF
    Energy called National Control to confirm that there was a problem on the network,
    and 17 minutes later National Control called back offering to restore supplies to
    Wimbledon and New Cross.

128 Such operational communications continued throughout the restoration, with
    numerous telephone conversations between National Control engineers and EDF
    Energy’s control engineer, working together to reconnect the affected area.

129 Following the restoration of supply, communications with the control rooms continued
    as further reconfiguration of the systems took place to ensure full security was
    restored.

130 During the incident National Control managers were confident that this was a system
    incident and this was confirmed to New Scotland Yard at 18.51.


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National Grid Company plc                                     10 September 2003

131 From Thursday evening and over the next day, National Grid gave working level and
    senior level briefings to DTI (including the Energy Minister), Ofgem, the Mayor of
    London, energywatch and many others with a direct interest.

132 National Grid began responding to the very large number of media calls within 25
    minutes of the start of the incident through its communication procedures. Senior
    executives from the company were available for media interview between late
    Thursday evening and early Saturday morning.

133 The investigation has found a crucial factor in communications during the incident
    was that, although National Grid was able to restore supplies to its network within 30
    minutes, the various services to the public returned to normal in different timescales
    and in different ways. For example, after re-configuring the distribution network EDF
    Energy was able to restore supplies to some of its customers before supplies were
    restored by National Grid, but some of its customers could only be restored a short
    time afterwards. Disruption to rail services continued after power was restored due to
    timetables being disrupted and the evacuation of trains.

134 The prime route for communications with the public is generally through the standard
    channels of the providers of these services. For instance it would be through the
    customer call centre of EDF Energy and through the railway companies’ passenger
    information units. This was appropriate, as only these service providers could let the
    public know how the incident had affected their operations.

135 The providers of key services to the public, such as the underground and railway
    network operators, typically draw their electricity supplies from the local distribution
    network. During an incident involving loss of electricity supplies, including on the
    National Grid system, that would typically expect to communicate with the distribution
    company.

136 The investigation has found that further work is required as to whether
    enhanced communication between National Grid and the various organisations
    providing key services to the public during such a major incident would help
    them in making decisions on how to respond to the incident and communicate
    about their services with the public.


     Investigation

137 The planning of maintenance works had been carried out in accordance with National
    Grid’s policies and that the maintenance work could not be regarded as a cause of
    the incident. The investigation confirmed that the transmission system arrangement
    and the communication with the distribution system operator regarding this
    maintenance complied with the relevant National Grid planning standards and
    operating procedures.

138 All actions in configuring and switching the transmission system complied with
    National Grid’s planning standards and operating procedures and that the restoration
    process was carried out quickly and professionally without further incident. The
    response by control engineers to re-secure the network and restore the balance of


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National Grid Company plc                                     10 September 2003

     generation and demand ensured that the disturbance was contained within the
     affected substations.

139 The reason that the second fault occurred was that an incorrect protection relay was
    installed when old equipment was replaced in 2001. This incorrect installation was
    not discovered despite extensive quality control and commissioning procedures
    followed by both supplier’s and National Grid’s specialist staff. This piece of
    equipment has been replaced. Once the cause was known an extensive survey of
    similar equipment was immediately initiated. To date 20% (9,000 items) of this type
    of equipment on the National Grid system has been surveyed and there have been
    no similar cases. The remaining equipment will be surveyed within four weeks.

140 The engineers involved in the commissioning of the automatic protection equipment
    had the appropriate training, authorisation, experience and skills to undertake the
    task. There is evidence that the detailed commissioning procedures were followed
    correctly at all stages and that no part of the process had been omitted. However,
    the rating of the automatic protection equipment that is included on the
    documentation used for commissioning could have been more clearly visible to the
    commissioning engineers.

141 The actions to remove the Hurst transformer did not directly contribute to the cause
    of the incident. The consequential increase in flows on the Wimbledon to New Cross
    circuit, which were within operational limits, initiated the operation of the protection
    relay at Wimbledon. National Grid engineers would not expect their actions to
    remove the equipment would have caused the loss of supply.

142 The impact of the incident on the areas of south London was exacerbated by the loss
    of supplies to underground and railway transport services.

143 From the 20 July, EDF Energy’s distribution system was arranged such that a
    significant supply to London Underground was dependent on a single transmission
    circuit. This meant that in the event of a fault occurring on one of National Grid’s
    transformers at Wimbledon the distribution system configuration would result in a loss
    of supply. However, National Grid understands that EDF Energy had contingency
    arrangements for immediate restoration of supplies to London Underground in such
    an eventuality.

144 Following normal practice, during the incident there was extensive communication
    between National Control and the EDF Energy Control Centre, with both control
    rooms working effectively together during the incident.




                                            Page 25
National Grid Company plc                                   10 September 2003


     Actions being pursued

145 This is the largest loss of supply from National Grid for over ten years and the
    company has expressed its deep regret. This incident involved a number of other
    parties and National Grid will be working closely with them in the coming weeks to
    examine the consequences and identify improvements in systems or procedures.
    National Grid has reviewed its part in the incident and is committed to the following
    steps:

        ·   National Grid will work closely with other network operators to identify
            any improvements in co-ordination to enhance the overall security of
            electricity supplies, particularly to city centres and transport systems.

        ·   National Grid will work closely with EDF Energy, the Mayor, London
            Underground, NetworkRail and other London emergency and public
            service agencies to establish improved and more responsive
            communications in the event of major loss of supply.

        ·   National Grid is urgently surveying all installations as a further check on
            the integrity of the automatic protection equipment.

        ·   National Grid will carry out a further comprehensive investigation
            examining all aspects of the management of the protection systems so
            as to eliminate, as far as possible, the risk of incorrect installation or
            operation of automatic protection equipment.

        ·   National Grid will work to review operational procedures, and control
            room systems, including alarm presentation, in close consultation with
            Ofgem, DTI and other associated parties, to ensure that there is the right
            balance between safety risks and supply security.




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